A solid-state image sensing device is a photoelectric conversion element formed in an integrated circuit by using a technique of manufacturing a semiconductor device. As a transferring device for outputting charges generated by a photodiode as the photoelectric conversion element, a charge coupled device (CCD) or a CMOS device are used. Depending on the difference between the devices, an image sensor is called a CCD image sensor or a CMOS image sensor.
FIG. 37 is across section of a general CMOS image sensor. In the CMOS image sensor, a plurality of unit cells (pixels) are formed on an Si substrate 90. In each of the unit cells (pixels) in the CMOS image sensor, a color filter 94 is formed below a microlens 92. Through a metal wiring layer 96 below the color filter 94, light is focused in a photodiode 99 formed in a P-well 98 in the Si substrate 90. Some field effect transistors such as a transistor for transferring charges generated by the photodiode 99 and converting to voltage are formed on the semiconductor substrate for every unit cell. And those transistors are connected to wires of the metal wiring layer 96.
The CMOS image sensor has an amplification transistor for each pixel. Therefore it has a feature that occurrence of electric noise caused by reading of a photoelectric-converted electric signal is suppressed. Since mass production is possible by applying the LSI manufacturing process, the CMOS image sensor is cheaper than the CCD image sensor having a high-voltage analog circuit. The CMOS image sensor has advantages such that, since the device is smaller, power consumption is low, and no smear or blooming occurs in principle. In recent years, utilizing the feature, the CMOS image sensor is applied to a cellular phone or a high-grade digital single-lens reflex camera.
One of important development challenges of a CMOS image sensor is increase in sensitivity. For higher sensitivity, scaling down of a pixel is effective means. By using the wiring technique in the LSI field, wires at a 1.5 μm pitch or less can be manufactured. However, there is limitation in diffraction of light which occurs when light passes through a metal wiring layer and is focused on the photodiode. It is therefore expected to become difficult to realize scaling down of a pixel itself, when the size of a pixel becomes smaller than 1.5 μm.
To solve the problem, a backside illumination CMOS image sensor has been proposed in recent years. By using this method, light is not focused through the metal wiring layer, so that the problem of the diffraction limitation can be avoided. In addition, the region of the photodiode in a pixel can be sufficiently assured, and a pixel can be miniaturized to the size of about the wavelength of light. However, even when a backside illumination CMOS image sensor is employed, it is difficult to make a pixel smaller than 0.6 μm as the wavelength of red light.
There is an image correcting technique as a technique for realizing a higher-precision image without increasing the number of pixels. In the technique, correction such as successive complementation, edge reinforcement, or the like on a signal of each pixel by software or hardware means is performed to make an output image closer to a real object.
JP-A 2008-54754 (KOKAI) discloses a technique for correcting an image by hardware means using a nonlinear device.